In one of the deadliest days for foreign forces in Afghanistan this year, eight NATO troops were killed in three separate incidents Saturday, authorities said.
Three died in two separate bomb attacks in the south, according to North Atlantic Treaty Organization statements. The nationalities of those killed were not immediately released.
Earlier in the day, five NATO service members and four Afghan soldiers were killed in a suicide attack by a Taliban bomber who dressed like an Afghan soldier to infiltrate a joint Afghan-U.S. base on the edge of the eastern province of Laghman.
A Taliban spokesman has said the group plans to target Afghan officials, including security forces, allied with NATO and the U.S.
Attacks by insurgents wearing Afghan security forces uniforms are not uncommon, but the death toll from such incidents has not been as high recently. In November 2010, six U.S. soldiers were killed by an insurgent posing as an Afghan border police agent at a military training area in Nangarhar province. The year before, five British soldiers in Helmand province were killed in a similar attack.
A senior U.S. military official Sunday said infiltration by Taliban agents in the security forces is a concern, but insurgents do not appear to be pursuing it as a strategy of late to the same extent as car bombs, suicide bombs and assassinations.
The official described the vetting process for Afghan security forces as "pretty exhaustive" and said it is continuously improving. In addition, NATO coalition forces have been training counterintelligence agents to isolate Taliban agents within the ranks, according to Lt. Gen. William B. Caldwell IV, who leads the U.S. and NATO training mission in Afghanistan.
Speaking in London last week, Caldwell said coalition forces expected to train about 445 agents.
"That will enable us to have a check and balance out there," Caldwell said, with "counterintelligence agents operating out there in support of the government of Afghanistan looking for anybody who may be trying to turn somebody or may have been an infiltrator."